1. Field of the Invention
The present invention relates to an image forming apparatus equipped with a sheet feed cassette.
2. Description of the Related Art
Heretofore, there has been known an image forming apparatus, such as a printer, equipped with a sheet feed cassette adapted to storably receive therein a plurality of sheets (recording sheets) and to be insertingly mounted in a sheet feed section of an apparatus body in a drawer-like manner. In connection with recent downsizing of OA apparatuses, for example, one type of image forming apparatus is widely prevalent which is designed to use a A4 sheet as a standard sheet, and arrange manual operating means, such as means for insertion/pullout of the sheet feed cassette and means for manual sheet feed, on the side of a front surface of an apparatus body in a concentrated manner so as to provide enhanced operationality thereof. In this type of image forming apparatus, a sheet feed roller and other associated component are arranged in the vicinity of the front surface of the apparatus body, and a sheet feed cassette is inserted into the apparatus body in such a manner that a front portion thereof becomes approximately flush with the front surface of the apparatus body.
There is one type of sheet, so-called “legal-size sheet” primarily used in the United States etc., which has a width approximately equal to that of the A-4 sheet and a height or length greater than that of the A-4 sheet. Generally, a sheet feed cassette for storably receiving therein the legal-size sheets has a longitudinal dimension greater than that of the apparatus body of the above type of image forming apparatus. Thus, for the purpose of adequately mounting this sheet feed cassette in the image forming apparatus, the apparatus body has a rear portion formed with an opening for allowing a rear portion of the sheet feed cassette to protrude rearward therefrom. In this case, the exposed rear portion of the sheet feed cassette is likely to permit mote, dust and/or moisture to get into the apparatus body therefrom, resulting in occurrence of a disadvantage, such as void, thin spot or roll contamination. Moreover, if the sheet feed cassette is left for long periods of time, an exposed portion of a sheet stored in the sheet feed cassette will be disadvantageously discolored.
As measures for solving these disadvantages, there has been known a technique using a cover member attached around the opening of the apparatus body and adapted to be slidably or rotatably moved in conjunction with a protruding movement of the rear portion of the sheet feed cassette so as to cover an upper surface of the rear portion of the sheet feed cassette (see, for example, Japanese Patent Laid-Open Publication No. 05-51136).
The cover member as used in the above technique for the image forming apparatus is intended to prevent the intrusion of a foreign substance, such as dust, and therefore designed without taking particular account of measures against a phenomenon that, when the sheet feed cassette is mounted to protrude from the apparatus body, internal operating noises (such as sheet pickup noise, driving noise and sheet transport noise during a sheet feeding operation) of the apparatus body will leak outside through the sheet feed cassette and the opening. Thus, there is a problem that, when the sheet feed cassette is mounted to protrude from the apparatus body, the leakage of internal operating noises of the apparatus body becomes prominent.